The present invention relates to a signal communication system and, more particularly, to such a system which is particularly useful for indicating at a central location, the unauthorized disconnection of an electrical appliance, such as a television set, at any one of a plurality of locations, such as from an outlet in one of the rooms of a hotel or motel.
The theft of television sets and the like from hotel and motel rooms is becoming increasingly common. Because such thefts represent substantial financial losses for the owners of such establishments, many different apparatuses and arrangements have been developed in an attempt to prevent such thefts. For example, some hotel and motel owners utilize mechanical arrangements which physically secure the television set at its room location in a manner which either prevents or inhibits removal. Most of such physical arrangements, however, are not satisfactory because they generally restrict the location from which programs on the set are viewable and/or are often defeatable in the long span of time in which a potential thief has access to the same when the thief is a registered guest.
In view of the deficiencies of mechanical theft prevention devices, generally the art has turned to use of a signalling or communication system of one sort or another which provides a signal at a central location, such as in the manager's office, whenever a television set is disturbed or electrically disconnected from its location. The more effective of such systems have required, however, that separate wiring be installed to each of the television locations, i.e., to each of the rooms of the hotel or motel. It will be appreciated that the expense of such an installation is major, especially if the system is to be installed in a hotel or motel which has previously been constructed. Attempts have been made to circumvent this expense by utilizing the existing electrical power distribution network of a hotel or the like as a communication link between the various television sets and a central location. The theft communication systems described in U.S. Pat. Nos. 3,411,150; 3,482,243, and 3,484,775 are examples of such systems. The use of electrical power lines for this purpose, however, has been found not to be satisfactory. For one thing, no such system has yet been developed which effectively prevents power surges or drains caused by the usual connection of various and sundry tools, appliances, etc., to the power line from adversely affecting the correct operation of the theft communication system. Moreover, the division of the power lines in the building into various circuits often restricts or prevents communication between certain locations. Such systems are also easily disabled without giving any clue to where a potential theft might take place, merely by interrupting the AC power.